Improvement in safety-valves



UNITED STATES PATENT OFFICE.

GEORGE II. CROSBY, OF SOMERVILLE, MASSACHUSETTS.

IMPROVEMENT I N SAFETY-VALVES.

Specification forming part of Letters Patent'No. 1515,157, dated January 26, 1875; application filed December 21, 1874.

'To all whom. it concern Be it known that I, GEORGE H. CROSBY, of Somerville, Middlesex county, and State of Massachusetts, have invented certain new and useful Improvements in Safety-Valves, of which the following is a specification, refereuee being had to the'accompanying drawing,

in which- Figure 1 is a vertical central section of a safety-valve embodying my invention. Fig. 2 is a plan of the same, with the valve proper, spring, and cross-head removed, for the pur-` pose of exposing the interior of the shell.

resistance to the lifting aetion'ot' the steam."

I connect with the primary valve a supplement-al valve, G, which is of less diameter than the'primary valve, and moves with the primary valve, which supplemental valve is within the shell, and in its normalpositionrests on a seat, H, by which the under face of the valve, when .in this position, is shielded from the action of the steam. Under this arrangement the steam under boiler pressure presses against the under face of the larger primary valve and the upper face of the smaller supplemental valve; consequently the lifting force exerted by the steam isequal to the number of pounds pressure per square inch on the-boiler multiplied by the diil'erence between the areas of lthe exposed surfaces of the two valves. `When this product exceeds the resistance offered by the spring C the pri mary valve will'rise; but in so doing it lifts the supplemental valve from its seat, and steam is admitted below the under surface of the latter valve. The surface upon which the lifting force of the steam can act is in this way increased by an amount equal to the area of the supplemental valve, aiuhconsequently increased 'power is obtained to open the primary valve still wider against the resistance of the spring, which resistance, of course, in-

creases in proportion to the compression of area of the discharge-outlets is, preferably, f

less than the area of the opening into the chamber closed by the supplemental valve. This arrangement can be effected ,in various ways. The chamber l ls within the shellA, and steam passes freely up around it to the primary valve. Under this arrangement', when the primary valve is lifted, and withit t-he supplemental valve, of course, the increased lifting power of the steam will be governed by the difference between the area of the supplemental valve and lthe areas of the discharge-outlets; and the steam will escape in two directions up through the main exit around the primary valve, and down through the chamber I and outlets J.

The above-described arrangement renders it feasible to vary the reduction in the nuin her of pounds pressureefectedbythe blow.-

ving off of thevalve Without the removal of any part from the boiler, and even while the valve is under pressure; and, further, the valve can be immediately adjusted from Work' ing properly at a high pressure t'o Working properly at a low pressure, and vice versa. The results I attain by providing one or more of the discharge-outlets J with stop-'cocks K, bushings, or other suitable means for varying the' size of the opening to which they are attached.' These devices may be so adjusted that Vthe steam cannot escape from the chamber I as fast as it enters it, and thereby the' supplemental valve is acted on by a dierential pressure, which, as above explained,

In conclusion, I-would state that alo not more of said outlets,to regulate the discharge of steam therefrom; substantially' as set forth. 2. In combination with the valve-shell and primary valve, une supplemental valve and chamber within the steam-space of the sheil,'

thedischarge-passages or outlets leading from said chamber through and out from the shell," and means, substantially as described, for

regulating the escape of steamA from said outlets for joint operation, as shown and set forth. In testimony whereof I have hereunto signer' my name this 18th day of Becemben, A. I

1874. f GEORGE H. 'GROSBX Witnesses z.

J. H. MILLETT, SAML. W. CLIFFORD, Jr.- 

